After pricing out some of the SS conicals out there i thought i could just kinda sorta maybe do it myself. Maybe. But after looking at the prices of the parts required i thought it would worth the experiment. Here's what i used:
$20 - 24ga stainless steel sheet, 304, 24"x48" (from the local metal supplier)
$17 - BCM14WLMP-G200, 2" tri-clamp ferrule (dump port)
$13 - BCM14WLMP-G100, 1" tri-clamp ferrule (racking port)
The end product was a SS conical with a 2" dump port, 1" racking port, 2" top port for wort fill/thermowell/blowoff (using the original sankey port).
2 vise grips
solder gun (not iron)
stainless flux (lennox)
step bit + drill
Keg prep: 30 min
I cut the *bottom* of the keg off with the angle grinder + cutting wheel at the weld seam and saved the bottom ring for the stand. Sand/grind down any rough areas. Prep the keg first so you'll have exact measurements for the cone.
research and calculations: 1 hr (should take you less with the info below)
The most mentally taxing portion of the job were the cone calculations. I found the following math instructor/prof's website extremely helpful as it's been a while since i took geometry.
Mr Wilson has a nice spreadsheet you can download. I wish everyone could use my numbers but every keg is a little different, where you cut the keg affects the cone, and cone/keg attachment method also affect the cone values. For me i cut out of the sheet an outer radius of 15.8", inner radius of 2", and 179 degrees. Note that 179 isn't 180 and 1 degree makes a difference a 16" away. But 179 is less than 180 so you can use part of the flat edge of the sheet from the factory.
sheet cutting: 1 hour
I cut the outer radius with tin snips, 24 is just thin enough to cut by hand. The inner radius was too tight to do by snips so i used a dremel. As you can see in the pics i did practice models with paper, good thing too as it took a few tries to get is just right (i found out my keg wasn't a round as i thought and initially used the shorter diameter for my cone calculations).
sheet bending: 1 hour
The next step was to bend the sheet into something resembling a cone. I just used gloves and SWMBO's kitchen rolling pin. Actually it was "ours" since it was a wedding gift. Anyways i spend the next few nights slowly bending the sheet in between diaper changes, etc. 5-10 minutes at a time.
cone soldering: 1-2 hour
Once the sheet is more or less cone-like, i lightly cleaned and sanded the edges to remove the oxide layer then clamped the two ends together with vise-grips. A light coating of flux and the solder adhered like a champ. I soldered inside and outside of the cone. Note that solder isn't the strongest joint but the addition of the ferrules + keg join will make it pretty durable. Just don't drop it. Also note that you can't use a electronics soldering iron, they just don't put put out enough heat. A torch will work as well but i liked the control of the soldering gun.
Ferrule/tri-clamp port additions: 1-2 hr
The ferrules come pretty long from JME so i shortened them down with a saw. I pre-wetted them (flux, solder) and the cone attachment areas to make sure i had a good bead. A few times in the past i noticed that i didn't quite clean an area and the solder didn't stick, pre-wetting (soldering) the areas tells me if i did it right without committing the entire joint, and it reduced the need for 1 less hand while doing the soldering (1 hand for the cone, 1 for the ferrule, and 1 for the solder wire). I placed the racking port in the middle of the cone joint to give the joint more strength, but the port also seemed the very delicate as there is significant leverage on the thin joint by the ferrule. I extended the ferrule 1/8" into the cone and added two strips of sheet on the outside across the cone joint to give the joint more strength.
Cleaning: 15 min
Thoroughly clean off all the flux! It starts doing weird things to the solder if you leave it on and it gets real hard to remove. You can remove burnt flux with fresh flux, and rinse it off with boiling water (per Lennox). Clean off the cone and ports as access later on is much harder.
Keg Join: 2 hr
I pre-wet all the joint areas for the cone/keg join as well. The harder part was getting the cone perfectly on and to stay still while i soldered. My keg wasn't perfect, and my cone was much less round than the keg. But the cone radius was larger than the keg opening (overlap) so i was able to insert the cone and pull up on it until it got stuck. It took a few times to get it just so. With the overlap there was a small gap above the keg/cone point of contact and i just filled it it with solder. The overlap was just over 1/4" for me so the joint is quite strong, it just takes a lot of solder to do. I opted for this overlapping joint instead instead of a butt joint primary for strength, but it was also significantly easier to do and is more forgiving in workmanship (of the cone and keg cut).
Final clean: 15 min
lots of hot water on the inside, maybe some PBW and/or oxyclean.
Things i would do differently:
1) I originally decided to solder the bits together as i could not reliably MIG the 24ga SS. Since doing the build i've dialed in my welding and would weld for strength, i am nervous when handling this conical. I'd grind down the nasty SS welds and probably solder over them for sanitary purposes. MIG welds can be especially porous and the solder would take care of that.
2) Yuri_rage has a DIY SS conical build too and i like what he did with the corny lid. That would make getting inside possible.
1) Cooling- I'm toying around with the idea of wrapping the keg with copper tubing and running cold water through it.
2) better stand. Right now the conical is on a wheeled stand made of out of 3/4" angle and the bottom keg ring. It's not as stable as i like. But it is portable and removable for storage.
1) solder joint strength. I'm reasonable confident in the joints. I accidentally dropped the completed conical on the cone without damage. I've filled it to the top without leaks. However i did drop the cone during construction and the joint did break. The ferrules and keg join provide stiffness that a rolled up piece of sheet metal cannot do on it's own.
2) sanitary- the same as a sankey fermentor.